Medical balloons have been widely used in medical procedures. Typically, an uninflated medical balloon is inserted into a body-space, e.g., blood vessel, urological vessel, etc. by means of a catheter. After positioning at the desired location within the body, the medical balloon is inflated by introducing a fluid into the balloon through the catheter under pressure. The inflation fluid causes the volume of the medical balloon to expand, and the adjacent body-space is similarly expanded. In procedures such as angioplasty, the inflated medical balloon may be used to open a collapsed or blocked artery. The fluid may then be withdrawn from the balloon, causing it to collapse to facilitate its removal from the body.
It is known to use medical balloons made of non-compliant materials for procedures where the dimensions of the inflated medical balloon must be uniform and predictable, even when different inflation pressures are used. Because the maximum diameter of such non-compliant balloons is predetermined, they are less likely to rupture or dissect the vessel or body-space when the balloon expands.
Before inflation, non-compliant medical balloons are typically folded tightly against the catheter in order to reduce the assembly's overall cross-section (i.e., to better fit through small body-spaces). It is thus normally desirable that the walls of the balloon be as thin as possible, so that the uninflated balloon will have the smallest diameter possible. However, medical balloons are increasingly being used to open body spaces restricted by tough tissues such as strictures, scarring or calcified areas. Stretching such tough tissue often requires the medical balloon to exert significant pressure. It is thus desirable that a medical balloon be capable of withstanding high pressure without rupturing. The pressure at which the walls of the balloon are expected to rupture is termed the “burst strength.”
In the pursuit of non-compliant medical balloons having both thin walls and high burst strength, it is known to make so-called “composite” balloons from a blow-molded thin film polymeric material having externally applied fiber-reinforcements. In some cases, such reinforcing fibers may be “filament wound” around the blow-molded “base” balloon in a simple helical fashion. In other cases, successive layers of fibers may be laid over the base balloon in adjacent, but separate (i.e., not woven together) layers having different orientations. While such fiber-reinforced balloons have resulted in improved performance compared to non-reinforced balloons, further improvement is desired. A non-compliant medical balloon having an integral non-woven fabric layer is disclosed in co-pending U.S. patent application Ser. No. 10/967,065 entitled “Non-Compliant Medical Balloon Having an Integral Non-Woven Fabric Layer,” filed Oct. 15, 2004, the disclosure of which is incorporated herein by reference for all purposes. A non-compliant medical balloon having an integral woven fabric layer is disclosed in co-pending U.S. patent application Ser. No. 10/966,970 entitled “Non-Compliant Medical Balloon Having an Integral Woven Fabric Layer,” filed Oct. 15, 2004, the disclosure of which is incorporated herein by reference for all purposes. A medical balloon having strengthening rods is disclosed in co-pending U.S. patent application Ser. No. 10/967,038 entitled “Medical Balloon having Strengthening Rods,” filed Oct. 15, 2004, the disclosure of which is incorporated herein by reference for all purposes.
“Braiding” refers to a system of fiber architecture in which three or more fibers are intertwined in such a way that no two fibers are twisted exclusively around one another. Braiding can be used to form fabric structures such as sheets, tapes, and even tubular sleeves having a continuous annular wall with a passage down the middle. The braided architecture resembles a hybrid of filament winding and weaving: As in filament winding, a tubular braid features seamless fiber continuity from end to end of a part; braided fibers are mechanically interlocked with one another. The resulting braid exhibits unique properties allowing it to be highly efficient in distributing loads. Specifically, because all the fibers within a braided structure are continuous and mechanically locked, a braid has a natural mechanism that evenly distributes load throughout the structure.
“Knitting” refers to a system of fiber architecture produced by intertwining threads in a series of interconnected loops rather than by weaving. In this fashion, the loops of fibers are mechanically interlocked. A weft-knitted structure consists of horizontal, parallel courses of fibers and requires only a single fiber. Alternatively, warp knitting requires one fiber for every stitch in the course, or horizontal row; these fibers make vertical parallel wales. Circular knitting refers to construction of a seamless tube whereas flat knitting is used to construct a flat structure.
The use of braided reinforcements for compliant medical balloons has been suggested. U.S. Pat. No. 5,647,848 to Jorgensen discloses a compliant medical balloon including an elastomeric balloon and a reinforcing structure that may include braided fibers. However, in such compliant balloons, the braid length and/or braid angle of the braided fiber structure changes between the deflated and inflated states, a condition that may be undesirable for non-compliant balloons.
A need therefore exists for a non-compliant medical balloon having braided fiber reinforcement. Preferably, the non-compliant braided fiber reinforced balloon will have a braid angle that does not change significantly between the deflated and inflated states.
A need further exists for a non-complaint medical balloon having knitted fiber reinforcement. Preferably, the non-compliant knitted fiber reinforced balloon will have knitted fibers that do not significantly change position relative to the surface of the base balloon between the deflated and inflated state.